Apparatuses, systems, and methods for dimming displays

ABSTRACT

Systems and methods are used to dim an emissive display such as an organic light emitting diode (OLED) display. A dimming level setpoint signal is received. At least one dimming process is selected from four dimming processes based on a magnitude of the dimming level setpoint signal. A first dimming process selects a subrange of pixel illumination levels from a range of pixel illumination levels. A second dimming process adjusts a VCOM voltage for the pixel array. A third dimming process selects between rolling shutter and global shutter. A fourth dimming process selectively utilizes one or more subpixels from an emissive display pixel based on the magnitude of the dimming level setpoint signal. The selected dimming process or processes are applied to the emissive display, there by dimming the display. The display can be an OLED display.

RELATED APPLICATIONS

This patent application claims priority from United States ProvisionalPatent Application titled: “APPARATUSES AND METHODS FOR DIMMINGDISPLAYS,” filed on Jun. 1, 2020, Ser. No. 63/033,139.

U.S. Provisional Patent Application Ser. No. 63/033,139 is herebyincorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates generally to displays and more specifically todimming Organic Light Emitting Diode (OLED) displays.

2. Art Background

OLED display technology is advancing at a rapid pace. In particular,development of high efficiency OLED materials as well as high throughputOLED deposition equipment has led to large scale commercialization ofOLED displays. An OLED device has organic semiconductor layers that aresituated between two electrodes, an anode and a cathode. The electrodesare typically made from inorganic materials. Holes and electrons areinjected to the organic layers from the anode and cathode, respectively.When the electrons and holes recombine in the active organic layer,photons are emitted.

A subset of OLED displays is micro OLED displays which are generallysmaller than 1 inch in diagonal size. Micro OLED displays typically havebackplane integrated circuits fabricated on a single crystal Silicon(Si) substrate. Because of the high performance of Si transistors, apixel size used to make a high-resolution display in a small size can bevery small, typically equal to or less than 15 micrometer (μm). Thebackplane circuitry includes a pixel array, row/column drivers, videoinput, video processing, and programmable control.

Micro OLED displays are considered as a leading display candidate fornext generation wearable products such as virtual reality (VR),augmented reality (AR), and mixed reality (MR) applications because oftheir small size and high resolution, low power consumption, and highvideo frame rate.

Some microdisplay applications require operation over a wide range ofbrightness depending on a given use case. For example, an augmentedreality (AR) display must be bright enough for acceptable visibility inoutdoor sunlight, yet also must operate at lower brightness forcomfortable viewing in dark indoor environments.

Existing transmissive and reflective display technologies (e.g., liquidcrystals or digital micromirrors) generally de-couple the light source(back-light or front-light) from the spatial light modulator (thedisplay panel itself). It is therefore straightforward to adjust thebrightness by controlling the light source, while the full dynamic rangeof the display is available to control individual pixels. However,display technologies such as OLED operate by modulating emission oflight at each pixel. Different dimming methods are needed to maintaindynamic range. This can present a problem.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. The invention is illustrated by way ofexample in the embodiments and is not limited in the figures of theaccompanying drawings, in which like references indicate similarelements. The patent or application file contains at least one drawingexecuted in color. Copies of this patent or patent applicationpublication with color drawing(s) will be provided by the Office uponrequest and payment of the necessary fee.

FIG. 1 illustrates multiple ranges of illumination informationconfigured for dimming an emissive display having a general number ofbrightness levels, according to embodiments of the invention.

FIG. 2 illustrates multiple ranges of illumination informationconfigured for dimming an emissive display having four states reservedfor brightness levels, according to embodiments of the invention.

FIG. 3 illustrates a flow diagram for dimming an emissive displayutilizing multiple ranges of illumination information, according toembodiments of the invention.

FIG. 4 illustrates a process for dimming an emissive display utilizingmultiple ranges of illumination information, according to embodiments ofthe invention.

FIG. 5 illustrates a flow diagram for dimming an emissive displayutilizing multiple ranges of VCOM levels, according to embodiments ofthe invention.

FIG. 6 illustrates a process for dimming an emissive display utilizingmultiple ranges of VCOM levels, according to embodiments of theinvention.

FIG. 7 illustrates rolling shutter with black line (K) trailing activeline (A) according to embodiments of the invention.

FIG. 8 illustrates rolling a shutter sequence with two frames and a 20%duty cycle, according to embodiments of the invention.

FIG. 9 illustrates a global shutter sequence with two frames and a 20%duty cycle, according to embodiments of the invention.

FIG. 10 illustrates a flow diagram for dimming an emissive displayutilizing multiple shutters, according to embodiments of the invention.

FIG. 11 illustrates a process for dimming an emissive display utilizingmultiple shutters, according to embodiments of the invention.

FIG. 12 illustrates, two subpixels with a 3:1 anode area ratio (Lshape), according to embodiments of the invention.

FIG. 13 illustrates, two subpixels with a 3:1 anode area ratio (Cshape), according to embodiments of the invention.

FIG. 14 illustrates, two subpixels with a 3:1 anode area ratio (Oshape), according to embodiments of the invention.

FIG. 15 illustrates, a pixel circuit diagram, according to embodimentsof the invention.

FIG. 16 illustrates, three subpixels with a 1:2:6 anode area ratio,according to embodiments of the invention.

FIG. 17 illustrates, a pixel circuit diagram corresponding to FIG. 16,according to embodiments of the invention.

FIG. 18 illustrates, a general number of subpixels (0 shape), accordingto embodiments of the invention.

FIG. 19 illustrates, a pixel circuit diagram corresponding to FIG. 18,according to embodiments of the invention.

FIG. 20 illustrates, a flow diagram for dimming an emissive displayutilizing multiple processes, according to embodiments of the invention.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings in which like referencesindicate similar elements, and in which is shown by way of illustration,specific embodiments in which the invention may be practiced. Theseembodiments are described in sufficient detail to enable those of skillin the art to practice the invention. In other instances, well-knowncircuits, structures, and techniques have not been shown in detail inorder not to obscure the understanding of this description. Thefollowing detailed description is, therefore, not to be taken in alimiting sense.

In various embodiments, apparatuses, methods, and systems are describedfor dimming emissive displays such as OLED displays. As used in thisdescription of embodiments, display and micro display are to be affordeda broad meaning and can be used interchangeably. Note that embodimentsof the invention are applicable to displays of various sizes includingmicro displays of 1.5 inch or less as measured across a diagonal of thedisplay to large flat panel displays measuring multiple feet across adiagonal of the display. Thus, embodiments of the invention areapplicable to displays of any size. Also, as used in this description ofembodiments, it will be understood that a pixel of an emissive displaysuch as an OLED display can be made from multiple subpixels, where eachsubpixel is used to contribute a separate color of light to the pixel.In addition, for the purpose of dimming a pixel can be divided into oneor more subpixels, where each subpixel used for dimming is made withsubpixels used for color. Thus, a pixel can be characterized by twolevels of subpixels, a first level used for dimming and then a secondlevel used for color. Note that the terms; “pixel,” “display pixel,”“display element,” or “OLED device” are used synonymously and all ofthese terms, i.e., “pixel,” “display pixel,” “display element,” or “OLEDdevice” are to be distinguished from “subpixel.” In addition, one ormore OLED pixels will be described in the figures that follow forclarity in the illustrations, however it will be understood that suchdescriptions extend to an entire display having many display pixelsconfigured in a row and many rows configured to provide displays havinga general number of m rows and n columns of OLED display elements onwhich images are provided to a user.

As used in this description of embodiments, the term “dimming ratio” isa magnitude of a display's white level, in the brightest configuration,divided by a magnitude of the display's white level in the least brightbut still useable configuration. As used in this description ofembodiments, the term “dynamic range” refers to the magnitude ratio ofthe white:black ratio of a display in a given configuration. That is,the magnitude ratio of the brightest and darkest pixel levels that canbe displayed at the same time. Either ratio may be convenientlyexpressed in orders of magnitude (powers of 10) or bits (powers of 2).Three orders of magnitude (1000) correspond roughly to 10 bits (1024).

In various embodiments, dimming ratios of 5 or 6 orders of magnitude (upto 20 bits) may be required in AR applications. Multiple techniques canbe used in combination to achieve particular requirements for a givendisplay.

One technique is useful in some cases when a display can achieve moredynamic range than is required for a given application. For example, ifthe display is capable of 12 bits of dynamic range and the applicationsrequire 10 bits, then 2 bits would remain available for dimming. In onenon-limiting example with linear encoding, the bright case would use1024 levels (0, 4, 8, . . . 4092), and a quarter-dimmed case would use1024 levels (0, 1, 2, . . . 1023).

FIG. 1 illustrates, generally at 100, multiple ranges of illuminationinformation configured for dimming an emissive display having a generalnumber of brightness levels, according to embodiments of the invention.As used in this description of embodiments, the term “illuminationinformation” flexibly refers to information that is used to producedifferent brightness from a pixel. Some non-limiting examples ofillumination information are, but are not limited to, a voltage or acurrent, an integer value in an array of values that correspond withvoltage, current, etc. that is used to provide different brightnessvalues from a pixel or a display made from an array of pixels.

With reference to FIG. 1, an array of illumination information isindicated at 102. A first range of illumination information spans arange from zero to Z as indicated at 104, Where zero representsillumination information that will produce a minimum pixel brightnessand Z represents illumination information that will produce a maximumpixel brightness. A second range of illumination information spans arange from zero to X as indicated at 106. Similarly, zero representsillumination information that will produce a minimum pixel brightnessand X represents illumination information that will produce a maximumpixel brightness for the range zero to X. Note that Z is greater than X,therefore the range of illumination values provided by 106 is less thanthe range of illumination values provided by 104. Therefore, a displayoperated by the range 106 will be dimmer than when the display isoperated by the range 104, Conversely stated the display operated by therange 104 will appear brighter than when the display is operated withthe range 106.

FIG. 2 illustrates, generally at 200, multiple ranges of illuminationinformation configured for dimming an emissive display having fourstates reserved for brightness levels, according to embodiments of theinvention. With reference to FIG. 2, a first range of illuminationinformation spans a range from zero to 4092 as indicated at 204. Wherezero represents illumination information that will produce a minimumpixel brightness and 4092 represents illumination information that willproduce a maximum pixel brightness. A second range of illuminationinformation spans a range from zero to 1023 as indicated at 206.Similarly, zero represents illumination information that will produce aminimum pixel brightness and 1023 represents illumination informationthat will produce a maximum pixel brightness for the range zero to 1023.If the illumination information follows a linear increase from valueszero to 4092, then the 206 will be one quarter as bright as the 204range. Two other ranges, the fifty percent bright case and theseventy-five percent bright case are contained within the range zero to4092 but are not indicated to preserve clarity in the illustration.

Note that in some embodiments, other multipliers (referred to herein asnon-integer multipliers) are used to provide different subranges of thefull range of illumination information shown above with the non-limitingexample using zero to 4092. For example, in the case illustrated in FIG.2, a forty (40) percent case is obtained by using a non-integermultiplier of 1.6 times the 1023 making the maximum value of the 40percent case 1637. Non-integer multipliers can introduce rounding whichcan lead to some differential non-linearity with respect to theillumination information represented by the resulting range. However,such differential nonlinearity can be acceptable to a user in variouscases.

The examples given herein are provided merely for illustration with nolimitation implied thereby. In some embodiments, 12 bits of dynamicrange are provided with a resulting range of illumination valuesspanning zero to 4095, where 4095=2¹²−1. In other cases, ranges arescaled. For example, a range of illumination information based on 10bits of dynamic range has a maximum value of 1023, where 1023=2¹⁰−1.Scaling the 10 bit range to 12 bits results in 4092 for a maximum valuefor the scaled range.

FIG. 3 illustrates, generally at 300, a flow diagram for dimming anemissive display utilizing multiple ranges of illumination information,according to embodiments of the invention. With reference to FIG. 3, adimming input 302 is input into a selection unit 304. In one or moreembodiments, the dimming input 302 is an output of control that is usedto adjust a brightness of a display. The selection unit 304 receives thedimming input 302 and uses the dimming input 302 to select between afirst range of illumination information 306 and up to a n_(th) range ofillumination information indicated at 308 by D1M_(N). The selecteddimming information is used to set parameters of the display 310 suchthat a brightness of the display results from the selected dimminginformation. Thus, the dimming input 302 can cause the display 310brightness to increase or decrease depending on values of the dimminginput 302. As used herein, the variable n can be either a discretevariable, capable of representing a fixed set of values, or it can be acontinuous variable that is not confined to a fixed set of discretevalues.

FIG. 4 illustrates, generally at 400, a process for dimming an emissivedisplay utilizing various ranges of illumination information, accordingto embodiments of the invention. With reference to FIG. 4, a processstarts at a block 402. At a block 404 a first range of illuminationinformation is represented. The first range of illumination informationcorresponds to a first display brightness level when used to operate adisplay. Successive ranges of illumination information are representedas indicated at 406 for the n_(th) range, where n is a general numberand depends on how much display brightness dynamic range is available tobe used for dimming. Parameter n will vary depending on a givenembodiment and can be either a discrete variable representing a fixedset of values or a continuous variable that is not confined to a fixedset of values. Specific examples given herein are provided merely forillustration and no limitation is implied thereby.

At a block 408, a range of illumination information, indicated byDIM_(i) is selected from the available ranges DIM₁ through DIM_(n),where i is selected from the range 1 through n. At a block 410, theselected illumination information from the block 408 is used to operatean emissive display. In one or more embodiments, the emissive display isan OLED display. The process ends at a block 412.

Another technique for dimming an emissive display is to adjust biasvoltages or currents common to the pixel array. In a voltage-drive OLEDdisplay, for example, the VCOM cathode voltage is adjusted to brightenor dim all pixels. Where VCOM is negative, a negative VCOM voltagecloser to zero 0 (e.g., −2 volts) produces a dimmer pixel, while anegative voltage further away from zero (e.g., −4 volts) produces abrighter pixel. However, the OLED electrooptical response to voltage isnonlinear, and each VCOM set point must be compensated for differently.

FIG. 5 illustrates, generally at 500, a flow diagram for dimming anemissive display utilizing multiple sets of VCOM levels, according toembodiments of the invention. With reference to FIG. 5, a dimming input502 is input into a dimming selection unit 504. VCOM1 at 506 representsa VCOM setting that corresponds to a particular pixel or displaybrightness. Similarly, an array of VCOM values are constructed with theM_(th) value represented at VCOM_(M). The selection unit 504 selects aVCOM value from the group 506 to 508 responsive to the dimming input502. Alternatively, the selection unit can be configured to calculate aVCOM value based on the dimming input 502. Since there is generally anon-linear relationship between VCOM and pixel brightness a mathematicalrelationship can be used to calculate a VCOM value responsive to thedimming input 502. The mathematical relationship is made from acalibration measurement between VCOM and a pixel brightness parametersuch as illumination intensity, etc. The VCOM value selected is thenused to operate the emissive display 510. In various embodiments, theemissive display 510 is an OLED display.

FIG. 6 illustrates, generally at 600, a process for dimming an emissivedisplay utilizing multiple VCOM levels, according to embodiments of theinvention. With reference to FIG. 6, a process starts at a block 602. Ata block 604 a first VCOM value is stored, i.e., VCOM₁. The first VCOMlevel, VCOM₁, corresponds to a first display brightness level when VCOM₁is used to operate a display. Successive VCOM values are stored asindicated at 606 for the M_(th) value, where M is a general number. At ablock 608 a VCOM value is selected from 602 through 604 based on adimming input. Alternatively at the block 608, as described above inconjunction with FIG. 5, a VCOM value can be calculated based on adimming input. Parameter M will vary depending on a given embodiment. Ata block 610, the selected VCOM value from the block 608 is used tooperate an emissive display. In one or more embodiments, the emissivedisplay is an OLED display. The process ends at a block 612. Specificexamples given herein are provided merely for illustration and nolimitation is implied thereby.

Another technique for dimming is shuttering. Shuttering operates in thetime domain and can be used for dimming control with a linear response.In various embodiments, a dimming method is provided using both rollingand global shutters.

Dimming with a Combination of Global and Rolling Shutters

Shuttering is a technique for controlling image persistence, that is,limiting the time, during which, pixels are kept in the bright state.For example, shuttering with 25% duty cycle means that pixels are black75% of the time and bright for 25% of the time.

FIG. 7 illustrates a rolling shutter image, generally at 700, with blackline (K) 706 trailing active line (A) 704 according to embodiments ofthe invention. With rolling shutter, each horizontal row of a display702 is driven to black some fixed time after it written with activevideo data. If the display is scanned from top to bottom, then therolling shutter may be implemented with a black line (K) trailing 706 anactive line (A) 704, as shown in FIG. 1, where a portion 708 of thedisplay is in an ON state while portions 710 and 712 are in an OFFstate. If row K 706 follows close behind row A 704, then the duty cyclewill be short, but if row K 706 lags far behind the active line A 704then the duty cycle will be long.

FIG. 8 illustrates a rolling shutter sequence, generally at 800, withtwo frames and a 20% duty cycle, according to embodiments of theinvention. Each of the two frames in FIG. 8, i.e., Frame period 1 at 802and Frame period 2 at 822 is illustrated qualitatively with five (5)views illustrating the progress of the dimming through each of the twoframes shown. Views 804, 806, 808, 810, and 812 depict Frame period 1802, Views 824, 826, 828, 830, and 832 depict Frame period 2 822. As anon-limiting example of rolling shutter implementation, rolling shutterrequires the K line to follow the A line by a whole number of lineintervals. The smallest interval will be a single line (A-K=1), and thenext brightest will be twice as bright (A-K=2). In one non-limitingexample, used only for illustration and with no limitation impliedthereby, a display with SXGA format (1280×1024) can be expected toachieve 10 bits of dimming via rolling shutter. Rolling shutter allowsthe display to be written continuously, and therefore does not requireincreased data rates.

FIG. 9 illustrates, generally at 900, a global shutter sequence with twoframes and a 20% duty cycle, according to embodiments of the invention.When global shutter is used, all or substantially all pixels areswitched simultaneously ON and OFF. Global shutter requires that theentire pixel array be written before the illumination or “flash” periodto turn the pixels ON. In the example illustrated in FIG. 9, given onlyfor illustration and with no limitation implied thereby, a first frameperiod is indicated at 902. The first frame period 902 includes an OFFtime 904, during which the display remains black as indicated at 908,lasting for eighty percent (80%) of the frame period 902 and an ON time906, during which the display is in an ON state as indicated at 910,lasting for 20% of the frame period 902. A 20% duty cycle indicated withan ON time 906 and an OFF time 904. results in 80% of the frame period902 available for writing image data to the display. Similarly, a secondframe period 912 includes an OFF time 914, during which the displayremains black, as indicated by 918, lasting for eighty percent (80%) ofthe frame period 912 and an ON time 916, during which time the displayis in an ON state as indicated at 920, lasting for 20% of the frameperiod 912.

The lower the duty cycle, the smaller the ON time and the larger theduty cycle the smaller the OFF time. For a 90% duty cycle, only 10% ofthe frame could be used for writing during the OFF time, necessitating a10-fold increase in peak input data rate during the OFF time.

Global shutter does not require the flash interval to be quantized inwhole row intervals. In some embodiments, global shutter can require amore complex pixel design, with one or more transistors added to controlthe flash timing.

In various embodiments, use of global shutter or rolling shutter dependson the desired duty cycle for a display. Rolling shutter is typicallyused with large duty cycles, up to 100%, and global shutter is typicallyused for short duty cycles, typically less than the blanking time. Theblanking time is the time between the end of a first frame and thebeginning of the display of the second frame. Note that global shuttercan be used for duty cycles that are longer than the blanking time. Whenthis scenario is used the displayed data will include some data from adifferent frame. This situation may or may not be objectionabledepending on the image content. For example, if a lower portion of thedisplay contains symbology data that does not change much frame-to-framethen mixing image data from two frames might not be noticeable. However,if there is a significant change in image data frame-to-frame thenmixing data from multiple frames might be noticeable and can be avoidedby limiting the use of global shutter to duty cycles that are less thanthe blanking time.

For example, in the aforementioned SXGA format with 1024 active rows,the VESA standard specifies an additional 42 blank rows, for 1066 totalrows. When the duty cycle is less than 42/1066 (approximately 3.9%),then it is advantageous to use global shutter. In the example above, itis the time needed to display 42 rows of image data. In one or moreembodiments, the minimum flash interval, as constrained by internalswitching delays, is less than one eighth of the line period, and theminimum global shutter duty cycle is less than ((1/8)/1066)=0.01%.Therefore, more than 13 bits of dimming may be achieved. Also,importantly, the same realization allows the global shutter duty cycleto be increased in tine increments based on the pixel clock, so that thesecond-dimmest setting is only slightly brighter than the minimum dutycycle setting.

In one or more embodiments, when the desired duty cycle falls betweenthat of the maximum global shutter (42/1066 in the SXGA example) and theminimum rolling shutter (1/1066), either method can be used.

In some implementations of dimming with multiple shutters, a givendimming value might not produce exactly the same dimming for both typesof shutter, hence in the transition from one shutter type to the other,an artifact such as a flicker might occur. Thus, if the same threshold(duty cycle value) is used to switch from rolling shutter to globalshutter as duty cycle is decreasing as is used to switch from globalshutter to rolling shutter as the duty cycle is increasing then if adimming control was toggling right at the duty cycle value a flickercould manifest and bother the user. This problem is mitigated by usingseparate duty cycle values for the switching thresholds. In one or moreembodiments, a hysteresis control may be used with the threshold forswitching from rolling shutter to global shutter set lower than thethreshold for switching from global shutter to rolling shutter.

One non-limiting example of a multiple threshold system configurationapplicable to the SXGA display example above is to set the transitionfrom rolling shutter to global shutter at a duty cycle of 2% and thetransition from global shutter to rolling shutter at a duty cycle of 3%.Other values are possible and the particular values are provided merelyfor illustration with no limitation implied thereby.

FIG. 10 illustrates, generally at 1000, a flow diagram for dimming anemissive display utilizing multiple shutters, according to embodimentsof the invention. With reference to FIG. 10, a dimming input 1002 isinput into a dimming selection unit 1004. Rolling shutter parameters at1006 are used for a range of dimming inputs 1002. Similarly, globalshutter parameters at 1008 are used for a range of dimming inputs 1002.The selection unit 1004 selects shutter parameters from 1006 to 1008responsive to the dimming input 1002. The shutter parameters selectedare then used to operate the emissive display 1010. In variousembodiments, the emissive display 1010 is an OLED display.

FIG. 11 illustrates, generally at 1100, a process for dimming anemissive display utilizing multiple shutters, according to embodimentsof the invention. With reference to FIG. 11, a process starts at a block1102. At a block 1104 rolling shutter parameters are established for agiven display. At a block 1106 global shutter parameters are establishedfor the given display. At a block 1108, either rolling shutter or globalshutter is selected for use in dimming the display. As described above,the type of shutter used depends on a desired dimming value and displayduty cycle. At a block 1110 the display is operated at the dimming valuewith the selected shutter appropriate for the dimming value. The processstops at the block 1112.

Dimming with Subpixels

In various embodiments, in the spatial domain, the emissive area of eachpixel can be controlled using subpixels for control of dimming, notingthat each subpixel can also contain individual subpixels used for colorgeneration. In some embodiments, color subpixels are divided intosubpixels used for dimming. This division provides simplification to thecircuits used to drive the subpixels, for example a common write deviceand a common storage device can be used across dimming subpixels withina given color subpixel. As used in this description of embodiments, theterms “segmented” and “sub” are used synonymously. For example,segmented pixel, subpixel, and segmented subpixel can refer to the samestructure. Note that in some embodiments, display information isprovided by using a single color referred to in the art as grayscale.Any color can be used to provide a “Grayscale” display such as but notlimited to gray, green, red, blue, etc. Subpixel dimming in the spatialdomain achieves linear dimming control,

In one or more embodiments, a nonlimiting example, given only as anillustration and with no limitation implied thereby utilizes twosubpixels with a brightness ratio of 3:1, but it is understood thatmultiple subpixels and other ratios may be used. FIG. 12 illustrates,generally at 1200, two subpixels with 3:1 area ratio, according toembodiments of the invention.

In an emissive display such as an OLED display, two subpixels drivenwith the same voltages may be expected to have brightness proportionalto their anode area. FIG. 12 shows, a pixel 1202 which has a firstsubpixel 1204 and a second subpixel 1206, together these two subpixelshave a 3:1 anode area ratio. In this configuration, the smaller subpixel1206 is shown as a square and the larger pixel 1204 is show with anL-shape. It is recognized that other shapes are possible and may bepreferred for other applications. In various embodiments, the subpixelstructure shown in FIG. 12 can be employed for a full color pixel whichis made using individual subpixels for color such as red, green, andblue subpixels or it can be used to provide a grayscale display.

Note that the larger subpixel 1204 is nominally L-shaped with two longsides. Bisecting lines placed perpendicular to each of the two longsides at a midpoint of each of the two long sides will intersect at acentral point. Similarly, bisecting lines placed perpendicular to twosides at a midpoint of each of two perpendicular sides of the smallersubpixel 1206 will intersect at a central point. The bisecting lines ofthe large subpixel 1204 are not collinear with the bisecting lines ofthe smaller subpixel 1206. Non-collinear bisecting lines result in thepoint of intersection of the bisecting lines for the larger subpixel1204 being shifted from the point of intersection of the bisecting linesfor the smaller subpixel 1206. A shift in the X direction is indicatedat 1210 (ΔX) and a shift in the Y direction is indicated at 1208 (ΔY).An L-shaped subpixel configuration results in a small image shiftoccurring in both the X and Y directions as indicated.

In operation, when both the larger subpixel 1204 and the smallersubpixel 1206 are in an ON state an array of pixels will appear asillustrated at 1230 for the L-shaped subpixel bright array. The dimmestsetting for the L-shaped subpixel array is achieved by placing thelarger subpixels, e.g., 1204 in the OFF state and the smaller subpixels,e.g., 1206 in the ON state as illustrated at 1260 for the L-shapedsubpixel dim array. A third brightness setting (not shown) is achievedby placing the larger subpixels, e.g., 1204 in the ON state and thesmaller subpixels, e.g., 1206 in the OFF state.

FIG. 13 illustrates, two subpixels with a 3:1 anode area ratio (Cshape), according to embodiments of the invention. With reference toFIG. 13, in this configuration, the smaller subpixel 1306 is shown as asquare and the larger pixel 1304 is show with a C-shape. It isrecognized that other shapes are possible and may be preferred for otherapplications. In various embodiments, the subpixel structure shown inFIG. 13 can be employed for a full color pixel which is made usingindividual subpixels for color such as red, green, and blue subpixels orit can be used to provide a grayscale display.

Note that the larger subpixel 1304 is nominally C-shaped with three longsides. Bisecting lines placed perpendicular to each of the two longsides, at a midpoint of each of the two long sides, will intersect at acentral point. Similarly, bisecting lines placed perpendicular to twosides at a midpoint of each of two perpendicular sides of the smallersubpixel 1306 will intersect at a central point. The bisecting lines ofthe large subpixel 1304 are not collinear with the bisecting lines ofthe smaller subpixel 1306. Non-collinear bisecting lines result in thepoint of intersection of the bisecting lines for the larger subpixel1304 being shifted from the point of intersection of the bisecting linesfor the smaller subpixel 1306. A shift in the X direction is indicatedat 1310 (ΔX). A C-shaped subpixel configuration results in a small imageshift occurring in only one direction, i.e, the X direction asindicated.

In operation, when both the larger subpixel 1304 and the smallersubpixel 1306 are in an ON state an array of pixels will appear asillustrated at 1330 for the C-shaped subpixel bright array. The dimmestsetting for the C-shaped subpixel array is achieved by placing thelarger subpixels, e.g., 1304 in the OFF state and the smaller subpixels,e.g., 1306 in the ON state as illustrated at 1360 for the C-shapedsubpixel dim array. A third brightness setting (not shown) is achievedby placing the larger subpixels, e.g., 1304 in the ON state and thesmaller subpixels, e.g., 1306 in the OFF state.

FIG. 14 illustrates, two subpixels with a 3:1 anode area ratio (Oshape), according to embodiments of the invention. With reference toFIG. 14, in this configuration, the smaller subpixel 1406 is shown as asquare and the larger pixel 1304 is show with an O-shape. It isrecognized that other shapes are possible and may be preferred for otherapplications. In various embodiments, the subpixel structure shown inFIG. 14 can be employed for a full color pixel which is made usingindividual subpixels for color such as red, green, and blue subpixels orit can be used to provide a grayscale display.

Note that the larger subpixel 1404 is nominally O-shaped with four longsides. Bisecting lines placed perpendicular to each of two long sides,at a midpoint of each of the two long sides, will intersect at a centralpoint. Similarly, bisecting lines placed perpendicular to two sides, ata midpoint of each of two perpendicular sides, of the smaller subpixel1406, will intersect at a central point. The bisecting lines of thelarge subpixel 1404 are collinear with the bisecting lines of thesmaller subpixel 1406. Collinear bisecting lines result in the point ofintersection of the bisecting lines for the larger subpixel 1304 and thepoint of intersection of the bisecting lines for the smaller subpixel1306 being the same. Thus, there is no image shift in either the Xdirection or the Y direction.

In operation, when both the larger subpixel 1404 and the smallersubpixel 1406 are in an ON state an array of pixels will appear asillustrated at 1430 for the O-shaped subpixel bright array. The dimmestsetting for the O-shaped subpixel array is achieved by placing thelarger subpixels, e.g., 1404 in the OFF state and the smaller subpixels,e.g., 1406 in the ON state as illustrated at 1460 for the O-shapedsubpixel dim array. A third brightness setting (not shown) is achievedby placing the larger subpixels, e.g., 1404 in the ON state and thesmaller subpixels, e.g., 1406 in the OFF state.

FIG. 15 illustrates, a pixel circuit diagram, according to embodimentsof the invention. With reference to FIG. 15, a circuit diagramrepresentative of a pixel with two subpixels, used for dimming, such asany of the subpixels illustrated in FIG. 12, FIG. 13, or FIG. 14 isillustrated. In the discussion that follows, when reference is made to acomplementary metal-oxide-semiconductor (CMOS) implementation nolimitation implied thereby. In various embodiments, the back-planecircuit architecture used to drive a pixel of an emissive displayutilizes a pair of write transistors (PMOS and NMOS) indicated by CMOSdevice 1512 to charge storage capacitor 1514 from column line 1506. Inwrite operation, control lines 1508 and 1510 are used to charge storagecapacitor 1514 to the voltage of column line 1506. Voltage on storagecapacitor 1514 permits current to flow through subpixel transistors 1516a and 1516 b. A first switch transistor 1522 a is operated by a controlline 1520 a. When the switch transistor 1522 a is switched ON, currentflows through the smaller emissive subpixel and light is emitted fromthe emissive area 1502 a of the smaller subpixel. The smaller subpixelcan be, for example, any of the smaller subpixels, such as 1206 (FIG.12), 1306 (FIG. 13) or 1406 (FIG. 14).

Similarly, a second switch transistor 1522 b is operated by a secondcontrol line 1520 b. When the second switch transistor 1522 b isswitched ON, current flows through the larger emissive subpixel andlight is emitted from the emissive area 1502 b of the larger subpixel.The larger subpixel can be, for example, any of the larger subpixels,such as 1204 (FIG. 12), 1304 (FIG. 13) or 1404 (FIG. 14).

When both switch transistors (1522 a and 1522 b) are in the ON state,light is emitted from both the smaller subpixel and the larger subpixel.This state is illustrated at 1230 (FIG. 12), 1330 (FIG. 13) or 1430(FIG. 14). In various embodiments, the illumination information,described in conjunction with the figures above, is used to establishthe voltages used for column line 1506.

Thus, in one or more embodiments, two subpixels share a common storagecapacitor 1514, and therefore the two subpixels will be driven to thesame level. Because there is only one storage node 1514 and one columnline Cn 1506, the two subpixels require no more power to drive thanwould a single pixel of the same total area. Separate switch transistors(1522 a and 1522 b) are driven by signals F1 n and F3 n, respectively.In bright mode, both switch transistors (1522 a and 1522 b) will beenabled, but in dim mode the switch transistor 1522 b for the largersubpixel will be kept off. In this way, the bright mode is 4 timesbrighter than the dim mode, and a 2-bit dimming ratio is achieved.

In one or more embodiments, the drive and switch transistors are scaledto match the anode area ratio, with the larger transistors drawn 3 timeslarger than the smaller, to provide the same current density in bothsubpixels. In yet other embodiments, the drive and switch transistorsare drawn with similar size for the subpixels. The size of the drive andswitch transistors can be adjusted as required by the constraints of agiven implementation of an integrated circuit for the subpixels.

The switch signals F3n and Fin are also used in global shutter mode toenable the pixels during the flash period.

FIG. 16 illustrates, generally at 1600, three subpixels with a 1:2:6anode area ratio, according to embodiments of the invention. Withreference to FIG. 16, in this configuration, the smaller subpixel 1608is shown as a square, the middle sized subpixel 1606 is shown as arectangle, and the larger subpixel 1604 is show as a rectangle. it isrecognized that other shapes are possible and may be preferred for otherapplications. It is also recognized that more than three subpixels canbe provided, as described herein. In various embodiments, the subpixelstructure shown in FIG. 16 can be employed for a full color pixel whichis made using individual subpixels for color such as red, green, andblue subpixels or it can be used to provide a grayscale display.

Various dimming states are possible with the three-element subpixelshown at 1600. A maximum brightness state is illustrated at 1630 whereall three subpixels (1608, 1606, and 1604) are in an ON state. A dimmeststate is illustrated at 1690 where only the smallest subpixels 1608 arein the ON state. One of several medium states is illustrated at 1660where the smallest subpixels 1608 and the middle sized subpixels 1606are in the ON state while the largest subpixels 1604 are in the OFFstate.

FIG. 17 illustrates, generally at 1700, a pixel circuit diagramcorresponding to FIG. 16, according to embodiments of the invention.With reference to FIG. 17, a circuit diagram representative of a pixelwith three subpixels, used for dimming, such as the subpixels of FIG. 16is illustrated. In the discussion that follows, when reference is madeto a complementary metal-oxide-semiconductor (CMOS) implementation nolimitation implied thereby. In various embodiments, the back-planecircuitry architecture used to drive a pixel of an emissive displayutilizes a pair of write transistors (PMOS and NMOS) indicated by CMOSdevice 1712 to charge storage capacitor 1714 from column line 1706. Inwrite operation, control lines 1708 and 1710 are used to charge storagecapacitor 1714 to the voltage of column line 1706. Voltage on storagecapacitor 1714 permits current to flow through subpixel transistors1716a, 1716 b, and 1716 c. A first switch transistor 1722 a is operatedby a first control line 1720 a. When the first switch transistor 1722 ais switched ON, current flows through the smallest emissive subpixel andlight is emitted from the emissive area 1702 a of the smallest subpixel.The smallest subpixel can be the subpixels, such as 1608 (FIG. 16).

Similarly, a second switch transistor 1722 b is operated by a secondcontrol line 1720 b. When the second switch transistor 1722 b isswitched ON, current flows through the middle sized emissive subpixeland light is emitted from the emissive area 1702 b of the middle sizedsubpixel. The middle sized subpixel can be for example 1606 (FIG. 16).

Similarly, a third switch transistor 1722 c is operated by a thirdcontrol line 1720 c. When the third switch transistor 1722 c is switchedON, current flows through the largest emissive subpixel and light isemitted from the emissive area 1702 c of the largest subpixel. Thelargest subpixel can be for example 1604 (FIG. 16).

In one or more embodiments, the drive and switch transistors are scaledto match the anode area ratio, with the larger transistors drawn 6 timeslarger than the smaller, to provide the same current density in all ofthe subpixels. In yet other embodiments, the drive and switchtransistors are drawn with similar size for all of the subpixels. Thesize of the drive and switch transistors can be adjusted as required bythe constraints of a given implementation of an integrated circuit forthe subpixels.

The switch signals F1 n (1720 a), F2 n (1720 b), and F6 n (1720 c) arealso used in global shutter mode to enable the subpixels during theflash period. In various embodiments, the illumination information,described in conjunction with the figures above, is used to establishthe voltages used for column line 1706.

FIG. 18 illustrates, generally at 1800, a general number of subpixels(O-shape in this example), according to embodiments of the invention.With reference to FIG. 18, a pixel 1802 is constructed with a generalnumber of O-shaped subpixels. A first non-emissive area 1804 defines thegeometry of the pixel. A first subpixel 1806 is defined by a secondnon-emissive area 1808 and the first non-emissive area 1804. Similarly,a second subpixel 1810 is defined by the second non-emissive area 1808and a third non-emissive area 1812. Finally, a general subpixel 1818 isdefined by last emissive area 1816. Thus, a general number of subpixelsare created for a given pixel. Note that subpixel shapes other than theO-shape shown in FIG. 18 are used in other embodiments.

FIG. 19 illustrates, generally at 1900, a pixel circuit diagramcorresponding to FIG. 18, according to embodiments of the invention.With reference to FIG. 19, a circuit diagram representative of a pixelwith a general number m of subpixels, used for dimming, such as thesubpixels of FIG. 18 is illustrated. In the discussion that follows,when reference is made to a complementary metal-oxide-semiconductor(CMOS) implementation no limitation implied thereby. In variousembodiments, the back-plane circuit architecture used to drive a pixelof an emissive display utilizes a pair of write transistors (PMOS andNMOS) indicated by CMOS device 1912 to charge storage capacitor 1914from column line 1906. In write operation, control lines 1908 and 1910are used to operate CMOS device 1912 to charge storage capacitor 1914 tothe voltage of column line 1906. Voltage on the storage capacitor 1914permits current to flow through subpixel transistors 1916 a through 1916m. A first switch transistor 1922 a is operated by a first control line1920 a. When the first switch transistor 1922 a is switched ON, currentflows through the smallest emissive subpixel and light is emitted fromthe emissive area 1902 a of the smallest subpixel. The smallest subpixelcan be a subpixel, such as, 1818 (FIG. 18).

Similarly, an M_(tn) switch transistor 1922 m is operated by an M_(tn)control line 1920 m. When the M_(tn) switch transistor 1922 m isswitched ON, current flows through the M_(tn) emissive subpixel andlight is emitted from the emissive area 1902 m of the M_(th) subpixel.The M_(tn) subpixel can be for example 1806 (FIG. 18).

In one or more embodiments, the drive and switch transistors are scaledto match the anode area ratio, with the larger transistors drawn m timeslarger than the smallest, to provide the same current density in all ofthe subpixels. In yet other embodiments, the drive and switchtransistors are drawn with similar size for all subpixels. The size ofthe drive and switch transistors can be adjusted as required by theconstraints of a given implementation of an integrated circuit for thesubpixels.

The switch signals F1n (1920 a) through F1mn (1920 m) are also used inglobal shutter mode to enable the pixels during the flash period. Invarious embodiments, the illumination information, described inconjunction with the figures above, is used to establish the voltagesused for column line 1906.

In various embodiments, multiple dimming techniques are applied to anemissive display such as an OLED display, depending on a desired amountof dimming that is desired for the given display and application.

FIG. 20 illustrates, generally at 2000, a flow diagram for dimming anemissive display utilizing multiple processes, according to embodimentsof the invention. With reference to FIG. 20, a dimming input 2002 isinput into a dimming logic/control unit 2004. One or more of the fourdimming techniques described above are selected by the dimminglogic/control unit 2004 and are used to dim an emissive display 2014. Afirst dimming technique 2006 utilizes a portion of the dynamic range ofthe pixel brightness for dimming. A second dimming technique 2008adjusts VCOM across all pixels for dimming. A third dimming technique2010 selects a shutter method, ie., rolling shutter or global shutter. Afourth dimming technique 2012 adjusts an emissive area of the displaypixels by turning ON or OFF subpixels.

The four dimming techniques 2006, 2008, 2010, and 2012 can be usedindividually or in any combination to dim pixels of an emissive displaysuch as an OLED display. In some use cases, a display is used in verylow back light environments, such as those that exist during nighttimeor in a room with poor light or no light. In such low ambient lightenvironments, a display can be used to provide image information from anight vision camera, for example, that a user cannot see with the nakedeye. In this environment, it is desirable to maximize the dynamic rangeof the display while taking care not to blind the user with displaybrightness that is set too high. Thus, in some embodiments, the process2006 would not be used in order to maximize dynamic range in order torender the image information. The process 2008 would use a less negativeVCOM voltage perhaps −1.5 volts to −2 volts to dim the pixels. Process2010 would be set to global shutter with a short duty cycle to dim thepixels. The process 2012 would be set to the minimum subpixel area or asubpixel area at the low end. Configured as such, the display could beused for night vision to provide high dynamic range images while notblinding the user with a display that is too bright.

At the other end of the spectrum is the use case of full sunlight, wherethe display is used in broad daylight. Thus, in some embodiments, inthis use case, the display might be used to display symbologyinformation to a user, such as alpha numeric characters instead of imageinformation (e.g., land topography). Dynamic range can be sacrificed,only the high end or equivalently stated, the bright end of the dynamicrange is needed to display alpha numeric symbology characters. Thus, theprocess 2006 is used to give up some dynamic range in order to increasedisplay brightness. Only a few bits of dynamic range are needed. Theprocess 2008 is used to increase the brightness of the display pixels bymaking VCOM more negative. In some embodiments, this means making VCOMapproximately equal to, for example, −4 volts. The process 2010 operatesthe display at a high duty cycle, using for example rolling shutter tocontribute to display brightness. The process 2012 is set to enable fullpixel area to contribute to display brightness.

Thus, in various configurations techniques for dimming are combined toprovide very large ranges of dimming for emissive displays such as OLEDdisplays. Note that other combination of dimming techniques listed abovecan be combined in various embodiments of the invention. Two use caseswere described, one for night mode and the other for day mode, howeveras the ambient light level changes, the four dimming processes 2006,2008, 2010, and 2012 are used in various combinations and configurationsto provide a display that communicates information to a user withoutblinding the user or rendering the information unintelligible.

In various embodiments, the components of the OLED systems as well asthe OLED systems described in the previous figures are implemented in anintegrated circuit device, which may include an integrated circuitpackage containing the integrated circuit. In some embodiments, thecomponents of systems as well as the systems are implemented in a singleintegrated circuit die. In other embodiments, the components of systemsas well as the systems are implemented in more than one integratedcircuit die of an integrated circuit device which may include amulti-chip package containing the integrated circuit. In someembodiments, an OLED display and the OLED display backplane circuitryare implemented on the same integrated circuit chip.

For purposes of discussing and understanding the embodiments of theinvention, it is to be understood that various terms are used by thoseknowledgeable in the art to describe techniques and approaches.Furthermore, in the description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the embodiments of the present invention. It will beevident, however, to one of ordinary skill in the art that embodimentsof the present invention may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form, rather than in detail, in order to avoidobscuring embodiments of the present invention. These embodiments aredescribed in sufficient detail to enable those of ordinary skill in theart to practice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical, electrical,and other changes may be made without departing from the scope ofembodiments of the present invention.

Some portions of the description may be presented in terms of algorithmsand symbolic representations of operations on, for example, data bitswithin a computer memory. These algorithmic descriptions andrepresentations are the means used by those of ordinary skill in thedata processing arts to most effectively convey the substance of theirwork to others of ordinary skill in the art. An algorithm is here, andgenerally. conceived to be a self-consistent sequence of acts leading toa desired result. The acts are those requiring physical manipulations ofphysical quantities. Usually, though not necessarily, these quantitiestake the form of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, waveforms, data, time series or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the discussion, it isappreciated that throughout the description, discussions utilizing termssuch as “processing” or “computing” or “calculating” or “determining” or“displaying” or the like, can refer to the action and processes of acomputer system, or similar electronic computing device, thatmanipulates and transforms data represented as physical (electronic)quantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission, or display devices.

It is to be understood that various terms and techniques are used bythose knowledgeable in the art to describe communications, protocols,applications, implementations, mechanisms, etc. One such technique isthe description of an implementation of a technique in terms of analgorithm or mathematical expression. That is, while the technique maybe, for example, implemented as executing code on a computer, theexpression of that technique may be more aptly and succinctly conveyedand communicated as a formula, algorithm, mathematical expression, flowdiagram or flow chart. Thus, one of ordinary skill in the art wouldrecognize a block denoting A+B=C as an additive function whoseimplementation in hardware and/or software would take two inputs (A andB) and produce a summation output (C). Thus, the use of formula,algorithm, or mathematical expression as descriptions is to beunderstood as having a physical embodiment in at least hardware and/orsoftware (such as a computer system in which the techniques of thepresent invention may be practiced as well as implemented as anembodiment).

Non-transitory machine-readable media is understood to include anymechanism for storing information in a form readable by a machine (e.g.,a computer). For example, a machine-readable medium, synonymouslyreferred to as a computer-readable medium, includes read only memory(ROM); random access memory (RAM); magnetic disk storage media; opticalstorage media; flash memory devices; except electrical, optical,acoustical or other forms of transmitting information via propagatedsignals (e.g., carrier waves, infrared signals, digital signals, etc.);etc.

Thus, embodiments of the invention can be used to provide a dimmablehigh brightness OLED display. Some non-limiting examples of OLED systemswhere embodiments of the invention are used are, but are not limited to;mobile phone, large screen displays, use in a near-to-eye (NTE) displayor a headset computing device. Other embodiments of the invention arereadily implemented in a wearable or a head wearable device of generalconfiguration, such as but not limited to; wearable products such asvirtual reality (VR), augmented reality (AR), mixed reality (MR);wristband, watch, glasses, goggles, a visor, a head band, a helmet, etc.or the like. As used in this description of embodiments, wearableencompasses, head wearable, wrist wearable, neck wearable, thus any formof wearable that can be applied to a user.

As used in this description, “one embodiment” or “an embodiment” orsimilar phrases means that the feature(s) being described are includedin at least one embodiment of the invention. References to “oneembodiment” in this description do not necessarily refer to the sameembodiment; however, neither are such embodiments mutually exclusive.Nor does “one embodiment” imply that there is but a single embodiment ofthe invention. For example, a feature, structure, act, etc. described in“one embodiment” may also be included in other embodiments. Thus, theinvention may include a variety of combinations and/or integrations ofthe embodiments described herein.

While the invention has been described in terms of several embodiments,those of skill in the art will recognize that the invention is notlimited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

What is claimed is:
 1. A segmented organic light emitting diode (OLED)display pixel comprising: at least a first emissive area; at least asecond emissive area; and a non-emissive area, the non-emissive area isdisposed between the at least the first emissive area and the at leastthe second emissive area.
 2. The segmented OLED display pixel of claim1, wherein the at least the first emissive area is larger than the atleast the second emissive area, in operation in an ON state, a firstbrightness of the at least the first emissive area is larger than asecond brightness of the at least the second emissive area.
 3. Thesegmented OLED display pixel of claim 1, wherein in operation when theat least the first emissive area is in an ON state and the at least thesecond emissive area is in an ON state, a third brightness is providedand the third brightness is greater than either of the first brightnessor the second brightness.
 4. The segmented OLED display pixel of claim1, wherein a write device is used to provide common pixel illuminationinformation for the at least the first emissive area and the at leastthe second emissive area.
 5. The segmented OLED display pixel of claim4, wherein the write device is a CMOS device.
 6. The segmented OLEDdisplay pixel of claim 1, wherein a storage device is used to providecommon pixel illumination information for the at least the firstemissive area and the at least the second emissive area.
 7. Thesegmented OLED display pixel of claim 6, wherein the storage device is acapacitor.
 8. The segmented OLED display pixel of claim 4, wherein afirst switch line is used to place the at least the first emissive areain and out of an ON state and a second switch line is used to place theat least the second emissive area in and out of an ON state.
 9. Thesegmented OLED display pixel of claim 1, wherein one major axis of theat least the first emissive area and one major axis of the at least thesecond emissive area are substantially collinear.
 10. The segmented OLEDdisplay pixel of claim 1, wherein two major axes of the at least thefirst emissive area and two major axes of the at least the secondemissive area are substantially collinear.
 11. The segmented OLEDdisplay pixel of claim 1, wherein neither major axis of the at least thefirst emissive area and neither major axis of the at least the secondemissive area is substantially collinear.
 12. A method for dimming anorganic light emitting diode (OLED) display pixel comprising: receivingas an input a dimming level setpoint signal; selecting a subrange ofpixel illumination information from a range of pixel illuminationinformation, wherein the range spans a greater range of brightnesslevels than the subrange spans, the selecting is based on a magnitude ofthe dimming level setpoint signal; and driving the OLED display pixelusing the subrange.
 13. A computer-readable storage medium storingprogram code for causing a data processing system to perform the stepscomprising: receiving as an input a dimming level setpoint signal; andselecting a subrange of pixel illumination information from a range ofpixel illumination information, wherein the range spans a greater rangeof brightness levels than the subrange spans, the selecting is based ona magnitude of the dimming level setpoint signal; and driving an OLEDdisplay pixel using the subrange.
 14. A method for dimming an organiclight emitting diode (OLED) display pixel comprising: receiving as aninput a dimming level setpoint signal; adjusting a VCOM voltage for theOLED display pixel based on the dimming level setpoint signal.
 15. Acomputer-readable storage medium storing program code for causing a dataprocessing system to perform the steps comprising: receiving as an inputa dimming level setpoint signal; and adjusting a VCOM voltage for anOLED display pixel based on the dimming level setpoint signal.
 16. Amethod for dimming an organic light emitting diode (OLED) displaycomprising: receiving as an input a dimming level setpoint signal;establishing a selected duty cycle based on the dimming level setpointsignal; utilizing rolling shutter to dim the OLED display when theselected duty cycle is in a range from a first low limit to a duty cycleof 100 percent; and utilizing global shutter to dim the OLED displaywhen the selected duty cycle is in a range from a second low limit to aminimum duty cycle for the OLED display.
 17. The method of claim 16,wherein the first low limit is equal to the second low limit and thefirst low limit is equal to a blanking time for the OLED display. 18.The method of clam 16, wherein the first low limit is used to switchfrom rolling shutter to global shutter when the duty cycle isdecreasing, the second low limit is used to switch from global shutterto rolling shutter when the duty cycle is increasing, the first lowlimit is less than the second low limit and both the first low limit andthe second low limit are less than a blanking time for the OLED display.19. The method of claim
 16. wherein an increment on the global shutteris established by a pixel clock period.
 20. A computer-readable storagemedium storing program code for causing a data processing system toperform the steps comprising: receiving as an input a dimming levelsetpoint signal; establishing a selected duty cycle based on the dimminglevel setpoint signal; utilizing rolling shutter to dim the OLED displaywhen the selected duty cycle is in a range from a first low limit to aduty cycle of 100 percent; and utilizing global shutter to dim the OLEDdisplay when the selected duty cycle is in a range from a second lowlimit to a minimum duty cycle for the OLED display.
 21. A method fordimming an organic light emitting diode (OLED) display comprising:receiving as an input a dimming level setpoint signal; selecting atleast one dimming process from the following four dimming processesbased on a magnitude of the dimming level setpoint signal:
 1. selectinga subrange of pixel illumination levels from a range of pixelillumination levels;
 2. adjusting a VCOM voltage for the OLED display;3. selecting between rolling shutter and global shutter;
 4. utilizingone or more subpixels from each OLED display pixel; and applying the atleast one dimming process to the OLED display, there by dimming the OLEDdisplay.
 22. The method of claim 21, further comprising: selecting atleast two dimming process from the four dimming processes based on amagnitude of the dimming level setpoint signal.
 23. The method of claim21, further comprising: selecting at least three dimming process fromthe four dimming processes based on a magnitude of the dimming levelsetpoint signal.
 24. The method of claim 21, further comprising:selecting all four dimming process, wherein a magnitude of the dimminglevel setpoint signal is used to configure the four dimming processes.25. A computer-readable storage medium storing program code for causinga data processing system to perform the steps comprising: receiving asan input a dimming level setpoint signal; selecting at least one dimmingprocess from the following four dimming processes based on a magnitudeof the dimming level setpoint signal:
 1. selecting a subrange of pixelillumination levels from a range of pixel illumination levels; 2.adjusting a VCOM voltage for the OLED display;
 3. selecting betweenrolling shutter and global shutter;
 4. utilizing one or more subpixelsfrom each OLED display pixel; and applying the at least one dimmingprocess to the OLED display, there by dimming the OLED display.
 26. Thecomputer-readable storage medium of claim 25, further comprising:selecting at least two dimming process from the four dimming processesbased on a magnitude of the dimming level setpoint signal.
 27. Thecomputer-readable storage medium of claim 25, further comprising:selecting at least two dimming process from the four dimming processesbased on a magnitude of the dimming level setpoint signal.
 28. Thecomputer-readable storage medium of claim 25, further comprising:selecting all four dimming process, wherein a magnitude of the dimminglevel setpoint signal is used to configure the four dimming processes.